Large parent rolls of raw material are presently rolled up on a reel after a web manufacturing process. The parent rolls, such as paper, tissue, composite, or like web, are prepared, stored and eventually transported for subsequent finishing and conversion to a final product. In a typical converting process, the parent roll is unwound at one end of a processing line, and is processed through the processing line to thereby convert the raw material, such as to shorter or narrower rolls of product; or to shape products from the raw material, to separate products from the raw material, and/or to combine the raw material with other input elements to thereby create a product or product pre-cursor.
At least one drawback in the present state of the art is that thickness or sheet caliper across parent rolls formed from uncreped through-air dried (UCTAD) sheets may vary undesirably due to the relatively large diameters of parent rolls. Although the caliper difference problem is practically unnoticeable in manufacturing conventional wet pressed tissue wound on conventional tissue machine (TM) reels, caliper difference is a significant problem in high bulk products.
Large diameters typically cause different compressive stresses to the sheets in the parent roll at the top of the roll and approaching the core of the roll, which can result in significant difference in sheet caliper even after the sheets are converted into a finished product form. In particular, caliper difference in parent rolls for high bulk soft tissue can result in significant differences in the consistency of finished rolls, which not only impacts on the real and perceived qualities of the product but can impair converting line runnability and production efficiency.
The present invention provides a system for controlling the caliper of a fibrous web during winding operations, an apparatus for controlling the caliper of a fibrous web and methods for increasing caliper control of a fibrous web. The component parts of the present invention are simple, reliable, and economical to manufacture, assemble, and use. Other advantages of the invention will be apparent from the following description and the attached drawings or can be learned through practice of the invention.
Notably, the fibrous web discussed herein, such as a tissue web used to manufacture a tissue product, can generally be formed by any of a variety of papermaking processes known in the art. In fact, any process capable of forming a paper web can be utilized in the present invention. For example, a papermaking process of the present invention can utilize adhesive creping, wet-creping, double-creping, embossing, wet-pressing, air-pressing, through-air drying, creped through-air drying, uncreped through-drying, as well as other steps in forming the paper web. Some examples of such techniques are disclosed in U.S. Pat. No. 5,048,589 to Cook, et al., U.S. Pat. No. 5,399,412 to Sudall. et al., U.S. Pat. No. 5,129,988 to Farrington. Jr. and U.S. Pat. No. 5,494,554 to Edwards, et al., which are incorporated herein by reference.
According to an aspect of the invention, a method for increasing caliper control of a cellulosic fiber-containing web as the web is wound onto a roll is disclosed. The method includes the step of winding a fibrous web onto a roll to form a wound product. Prior to begin wound, the web is conveyed through a nip. The nip is configured to apply a pressure to the web and to selectively decrease the caliper of the web by increasing the pressure. Specifically, the nip pressure is increased as the diameter of the wound product increases in order to compensate for the caliper reduction that occurs in the web near the center of the wound roll due to compressive forces that are excited on the web as the diameter of the roll increases.
In one aspect of the invention, the pressure may be applied manually via a set of calender rolls in which the calender rolls are incrementally moved toward the web as the parent roll is formed. For instance, the calender rolls may be controlled by a human operator to move the calender roll toward the web. This control could be accomplished in various ways (i.e., pneumatic and hydraulic cylinders, block and tackle weights, embossing wedges, etc.).
Alternatively, an open loop control of the nip pressure may be employed in which, for example, a mathematical computer algorithm automatically increases the pressure as functions of time, reel length or roll diameter. More specifically, the algorithm can be programmed to automatically adjust the nip pressure over time, with the use of, e.g., a flow meter, a length of passing web, or when a diameter is physically reached.
Another exemplary embodiment may incorporate an on-line caliper sensor to allow a closed-loop feedback control of web caliper. This aspect of the invention may be dependent on the building diameter of the parent roll, which may be determined by the steps of monitoring the caliper of the fibrous web with a sensing device and then adjusting the pressure based on measurements of the caliper from the sensing device. Optionally, the sensing device can be supplemented by a computer to automatically adjust the calender gap or nip pressure in precise micro-adjustments as a function of the building roll diameter D. Alternatively stated, a remote computer can be configured to send commands to adjust the calender roll in small increments toward the web as the diameter of the parent roll increases.
According to another aspect of the invention, nip pressure to a tissue may occur in a converting line as the tissue is being unwound from the parent roll and wound onto a secondary roll or onto a packaging roll. The method may comprise the steps of monitoring the caliper of the tissue with a sensor and controlling the pressure of, for instance, a calendering device, based on measurements of the caliper from the sensor. In effect, the monitoring and controlling steps form a closed-looped feedback similar to the foregoing closed-looped description.
Other aspects and advantages of the invention will be apparent from the following description and the attached drawings, or can be learned through practice of the invention.